Editor's note: This story is part of the WardsAuto digital archive, which may include content that was first published in print, or in different web layouts.

Check to see if pigs are flying. That's what we figured would happen before any 3-ton GMC Yukon SUV achieved 20 mpg (11.8 L/100 km) in city driving.

Yet that's the powertrain near-miracle delivered by General Motors Corp.'s all-new 2-Mode hybrid-electric system, essentially an electronic continuously variable transmission (CVT) augmented by two electric motors, fixed-gear capability and a highly optimized, 6.0L variant of GM's small-block V-8. The breakthrough, of course, is that city economy of 20 mpg - 21 mpg (11.2 L/100 km) for 2-wheel-drive models — is a 50% leap over the same vehicle powered only by a 5.3L V-8.

GM boasts the Yukon Hybrid is as efficient in city driving as a 4-cyl. Toyota Camry. GM believes hybrid-electric vehicle technology, initially at least, is best suited for the thirstiest vehicles, where efficiency enhancements make the most impact. The 2-Mode is a significant achievement.

ENGINE SPECS

Engine type: 6.0L OHV 90° V-8

Displacement (cc): 5,967

Block/head material: aluminum/aluminum

Bore × stroke (mm): 101.6 × 92.0

Horsepower (SAE net): 332 @ 5,100 rpm

Torque: 367 lb.-ft. (498 Nm) @ 4,100 rpm

Specific output: 55 hp/L

Compression ratio: 10.8:1

Electric motor/transmission: (2) 60-kW electric motors/300-volt NiMH battery pack (30 hp electric boost)

Assembly site (engine/transmission): Silao, Mexico/Baltimore, Maryland

Application tested: GMC Yukon Hybrid 4WD

Fuel economy, city/highway (mpg): 20/20